This invention relates to a brake force regulator for a motorcycle hydraulic brake system wherein a rearwheel brake and a front-wheel brake are adapted to be actuated by a pedal-operated master cylinder and another front-wheel brake is adapted to be actuated by a handoperated master cylinder, and wherein the pressure applied to the rear-wheel brake is adapted to be reduced by a brake force regulator dependent on the pressure generated by the hand-operated master cylinder.
A brake force regulator of this type is known from German Printed Patent Application Dt-OS No. 2,558,825. The prior known brake force regulator resembles conventional brake force regulators for passenger cars. By actuating the pedal-operated master cylinder, pressure is initially supplied to a front-wheel brake unreduced and to the rear-wheel brake reduced. If in addition the handoperated master cylinder is actuated, the pressure thereby generated counteracts the control force of the brake force regulator so that the latter reduces the pressure of the rear-wheel brake to a greater extent than if only the pedal-operated master cylinder were actuated. In this arrangement, the brake force regulator is so designed that the displacement travel of its stepped piston is sufficient to reduce the pressure in the rear-wheel brake by means of an increase in the pressure of a front-wheel brake.
The prior known brake force regulator has the functional disadvantage that its stepped piston may be displaced also when pressure is built up only by the hand-operated master cylinder, i.e., when only the hand brake, which acts on the front wheel, is actuated. The displacement of the stepped piston causes pressurized fluid to be drawn from the rear-wheel brake. As a result, a vacuum will occur in the rear-wheel brake which may draw in air and impurities which may result in a failure of the brake.